How much do car brakes contribute to global warming?

Unless you drive a hybrid with regenerative braking, almost all the kinetic energy that comes from burning gasoline is dissipated as heat when you apply the brakes to stop your car. It would be interesting to measure just how much heat is added to our atmosphere on a daily basis just from people stopping their cars.

I could come up with back-of-the-envelope number if I knew how many brake pads and shoes are sold worldwide each day, and on average how much braking energy each pad or shoe contained. Anybody have a ballpark number on either of those?

Update (2006-04-18): It occurred to me after I made this post that most of the energy that comes from burning gas to move a car eventually is dissipated as heat: through the engine block; through the exhaust; from the breakpads; from the stereo; etc. Focusing on just the braking part of it is rather pointless, so forget it.